Metathesis of cycloolefins

Metathesis of Cycloolefins. The same general catalysts which promote the ring-opening polymerization of cycloolefins are also effective in the olefin metathesis reaction in which acyclic internal olefins undergo a unique redistribution process (1, 2, 5, 6). 

In this paper we report the cross-metathesis of cycloolefins with ethylene (ethenolysis). We present the selective synthesis of linear silicon-containing a,o>olefins starting with norbomene derivatives containing alkyl-, amine- or alkoxy-substituted silicon moieties and ethylene (Scheme 2). 

This process allows the synthesis of a,co-diolefins by cross-metathesis of cycloolefins with ethylene. The reaction was first studied by Phillips who produced multi-tons of... 

Korshak, V V, and Turov, B. S., Synthesis of unsaturated oligomers by co-metathesis of cycloolefins with linear olefins, Vysokomol. Soedin., A22, 723, 1980. 

Ring-Opening Polymerization. Ring-opening polymerization of cycloolefins in the presence of tungsten- or molybdenum-based catalysts proceeds by a metathesis mechanism (67,68). 

V. Dragutan, A. T. Balaban, and M. Dimonie, Olefin Metathesis and Ring-OpeningPolymeris tion of Cycloolefins,John Wiley Sons, Ltd., Chichester, U.K., 1985. 

As pointed out in an earlier section, Katz and co-workers demonstrated that Casey s complex, (CO)5W=CPh2, could also be employed to initiate the metathesis of a-olefins (26) as well as the polymerization of certain cycloolefins (27, 63). 

This process is quite unexpected for another reason. The cyclobutene ring is highly strained, making this monomer one of the most easily polymerized of all the cycloolefins. Thus, the variety of catalysts effective for cyclobutene polymerization is much broader than that effective for metathesis of low-strained cycloolefins and acyclic olefins (73). Therefore, the recovery of monomeric cyclobutene rather than its respective polymer is remarkable and indicates the lack of substantial metathesis activity in the above retrocarbenation system. 

The diverse steric course of the metathesis of cyclic vs. acyclic olefins poses a dilemma. It stands to reason that once a cycloolefin monomer... 

Such reactions of cycloolefins are called metathesis polymerization by analogy with the transalkylidenation reaction of linear olefins which proceed under comparable conditions and in which the double bonds of the olefins are broken and new double bonds are formed (metathesis) ... 

Macrocyclization equilibrium data from metathesis reactions of cycloolefins are compared with predictions of a novel, simple RIS scheme for polyalkenes with at least three single bonds between adjacent double bonds. The predictions agree with experiment within the combined experimental errors, supporting the conformational models and confirming that macrocyclization equilibrium has indeed been established in the metathesis reactions. 

Ring-opening metathesis polymerization of cycloolefins,93-99 a reaction of significant practical importance (see Section 12.3), is catalyzed by a number of well-defined transition-metal complexes. Alkylidene and metallacyclobutane... 

Ivin KJ (1983) Olefin metathesis, Academic, New York Dragutan V, Balaban AT, Dinonie M (1985) Olefin metathesis and ring-opening polymerization of cycloolefins, Wiley, New York... 

Another type of metal-carbon bond, the metal carbene bond (with carbene of an electrophilic or nucleophilic character), appears to be the active bond in transition metal-based catalysts for the ring-opening metathesis polymerisation of cycloolefins. Such a bond, which is co-originated with metal by the sp2-hybridized carbon atom, possesses a a, n double bond character (Mt = C) [34,35], The enchainment of the coordinating cycloolefin at the active site... 

A characteristic feature of cycloolefin ring-opening metathesis polymerisation is alteration of the metal-carbon active bonds from the metal carbene a, n bond into metallacycle a bonds, and vice versa, as polymerisation progresses. It is worth mentioning, in this connection, that metallacyclobutanes can be successfully used as catalysts for this polymerisation [36,37]. 

Kricheldorf, H. R., Metathesis Polymerization of Cycloolefins , in Handbook of Polymer Synthesis, M. Dekker, New York, 1992, Part A, pp. 433-479. 

The above examples show that the ring-opening metathesis polymerisation of cycloolefins, even simple substituted bicyclic olefins, gives rise, in principle, to polymers with a very wide range of microstructures defined by the frequency and distribution of cis and trans vinylene units, m and r diads and h-h, t-t or h-t arrangements of cycloaliphatic units. 

There is a wide variety of transition metal compounds, ranging from group 4 (Ti) to group 8 metals (Ir), that can be applied as catalysts or catalyst precursors for the ring-opening metathesis polymerisation of cycloolefins. However, the most commonly used are W, Mo, Re and Ru compounds tungsten-based catalysts appeared to be the most effective. Other transition metal compounds such as Nb and Ta compounds have also often been used as catalysts, but especially for mechanistic studies [45]. 

Although this view is oversimplified and borderline metal carbene complexes have been isolated, this approach is convenient for discussing the activity of metal carbene species in the ring-opening metathesis polymerisation of cycloolefins. Calculations have predicted [81,82] and recent results have shown [83] that, in some systems, metal alkylidene reactivity is competitive with metal carbene reactivity, i.e. olefin metathesis is competitive with olefin cyclopropanation. 

Nucleophilic metal alkylidene complexes are more useful for promoting the metathesis polymerisation of cycloolefins than electrophilic metal carbenes. For instance, Br2(Me3CCH20)2W=CHCMe3 is a moderately active catalyst [75,89] that can be further activated by the addition of Lewis acids such as GaBr3 to... 

It is interesting that, to promote the ring-opening metathesis polymerisation of cycloolefins, metal carbyne complexes can also be used in such a case, the carbyne complex is rearranged to form the actual metal carbene complex [scheme (9)] capable of initiating the polymerisation [95] ... 

If one considers a general scheme of the ring-opening metathesis polymerisation of cycloolefins [scheme (22)], it involves complexation of the monomer molecule at the free coordination site, followed by an attack of the carbene carbon atom on the complexed monomer [46] ... 

Copolymerisation, which is often carried out in order to gain a better insight into the nature of polymerisation initiating and/or propagating species and to modify the properties of the polymeric products formed, has also been satisfactorily carried out in the case of cycloolefins. The ring-opening metathesis... 

Cycloolefins can be ring-open polymerised with a high degree of stereospecificity. Many poly(l-alkenylene)s prepared by metathesis polymerisation of cycloolefins are stereoregular polymers with presumably a cis or Irons configur-... 

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